Young children with fearful temperaments have been a major focus of research on individual differences because these children are believed to be at risk for the development of internalizing problems, such as anxiety disorders. Research and theory on the etiology of these disorders has focused, in part, on individual differences in the intensity of fear behaviors. However, the mechanisms by which individual differences in fear put children at risk for developing behavioral problems have not been fully established. This proposal focuses on a model that posits the dysregulation of fear behavior as one potential mechanism to the development of internalizing problems. Historically, research on extremely fearful children has focused on observations during a limited variety of threatening contexts, situations in which most children are expected to show some level of fear. However, extreme fear during a fear-eliciting context may or may not reflect dysregulation. Therefore, the proposed study addresses whether different novel contexts, varying in their level of threat, result in an average pattern of change among all children, and individual patterns of change in the expression of fear-related behaviors. Specifically, the goal of the study is to evaluate two definitions of dysregulated fear behavior: cross-situational consistency in fear behavior and fear behavior in nonthreatening contexts (Aim 1). Participants will be 80, typically developing, 24-month-old children. Children will be observed in 12 situations, and fear behaviors will be assessed during each. Of particular interest is the identification of children who fail to regulate fear behavior based on contextual demands (i.e., dysregulated fear). Finally, the validity of the two definitions of dysregulated fear will be evaluated via associations with cortisol and maternal report of behavior problem symptoms, with particular focus on internalizing symptoms (Aim 2). These results are expected to further our understanding of the developmental risk factors and etiology of internalizing disorders in children, with particular focus on individual differences in emotion regulation. Better understanding of these risk factors will help to identify appropriate treatment and possible prevention. [unreadable] [unreadable] [unreadable]